Electrical rotating machine control unit and power generation system

ABSTRACT

Because of the necessity of resolver for detecting a rotating position, which is very expensive, and noise suppression of the rotating position signal line on a doubly-fed machine, cost increase of the generator and reduced reliability due to possible failures are inevitable. In order to solve such problem, a generation system in the present invention is equipped with an exciter that estimates the slip frequency of the doubly-fed machine from each primary current I 1  and voltage V 1  and secondary current I 2  and voltage V 2  of the doubly-fed machine and excites the secondary of the doubly-fed machine at the estimated slip frequency.

CROSS-REFERENCE TO A RELATED APPLICATION

This application claims the benefit of the filing date of JapanesePatent Application Serial No. 2004-004900, filed on Jan. 13, 2004.

BACKGROUND OF THE INVENTION

The present invention relates to a rotating electrical machine controlunit and power generation system, particular to a control unit and powergeneration system of a doubly-fed machine.

Doubly-fed machine has conventionally been used as the generator for anaerogeneration system. It is a generator-motor, equipped with 3-phasewinding laid in slots provided at equal distance on the stator androtor, that is operated at variable speed by applying variable-frequencyalternating current power particularly to the secondary of thegenerator-motor. As disclosed in the Japanese Application PatentLaid-Open Publication No. Hei 05-284798 (hereinafter called the PatentDocument 1), the doubly-fed machine like the above has a resolver fordetecting a rotating position, slip frequency which is the differentialbetween the primary frequency and secondary frequency is calculated, andthe output is controlled by a power converter.

[Patent Document 1]

Japanese Application Patent Laid-Open Publication No. Hei 05-284798

SUMMARY OF THE INVENTION

According to the prior art, cost increase of the generator has beeninevitable because of the necessity of resolver for detecting a rotatingposition, which is very expensive, and noise suppression of the rotatingposition signal line. In addition, the reliability is lower because ofincreased chances of failure. The present invention is capable ofcontrolling a doubly-fed machine without using a rotor position sensorsuch as resolver, and accordingly cost increase due to the use of arotor position sensor such as resolver in a doubly-fed machine can beprevented.

A characteristic of the present invention is to calculate a commandvalue of the voltage to be applied to the rotor winding based on thevoltage of the stator winding, current of the stator winding, andcurrent of the rotor winding.

Another characteristic of the present invention is to calculate theinformation relating to the rotor position based on the voltage of thestator winding, current of the stator winding, and current of the rotorwinding.

Other characteristics of the present invention are explained in detailhereunder.

According to the present invention, cost increase due to the use of arotor position sensor such as resolver in a doubly-fed machine can beprevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a brief construction of an embodiment of thepresent invention.

FIG. 2 is a diagram showing an equivalent circuit of a doubly-fedmachine.

FIG. 3 is a diagram showing vectors based on FIG. 2.

FIG. 4 is a diagram showing part of a rotor position detector.

FIG. 5 is a diagram showing an embodiment of the generation systemaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the present invention is described hereunder, usingfigures. FIG. 1 is a diagram showing the overall construction of adoubly-fed machine drive system to which the present invention applies.

As shown in FIG. 1, a doubly-fed machine 4, mechanically connected witha power source 2, is a generator-motor, equipped with 3-phase windinglaid in slots provided at equal distance on the stator and rotor, thatis operated at variable speed by applying variable-frequency alternatingcurrent power particularly to the secondary of the generator-motor, thatis, a generator-motor which is controlled by comparing the primaryvoltage with a control variable in the alternating voltage control 44 soas to adjust the secondary voltage. The stator winding 5 of thedoubly-fed machine 4 is connected to the electrical power system 1 via aswitch 101.

The rotor winding 6 of the doubly-fed machine 4 is electricallyconnected with an exciter 7 and the rotor winding 6 is alternatinglyexcited by the exciter 7. The exciter 7 comprises an indirectalternating current converter, consisting of converter 8 and inverter 9,which once converts alternating current power to direct current powerand then converts the direct current power to the alternating power ofdesired frequency.

The converter 8 is controlled by a converter controlling apparatus 30that generates a gate signal based on the electric power system voltageV₁ detected by a system voltage detector 21, output voltage of theconverter 8 detected by a current detector 26, and direct currentvoltage V_(dc) of the exciter 7.

The inverter 9 is driven by a gate signal generated by a PWM modulator50. This gate signal is generated in the circuitry explained below. Thesecondary current I₂ of the doubly-fed machine (current through thestator winding) detected by an exciting current detector 25 is convertedinto I_(α) and I_(β) by a 3-phase/2-phase converter 41, and the d-axiscurrent and q-axis current exhibited on a dq-axis rotating coordinatewhen the rotor position θ_(s) obtained from a rotating positioncalculator 20 is transformed in terms of the coordinate by a rotatingcoordinate transformer 42 are called I_(d) and I_(q), respectively. Whenthe rotor position θ_(s) is in the same phase as with the inducedelectromotive force due to slip, the d-axis current I_(d) represents theexcitation component and the q-axis current I_(q) represents the torquecomponent.

A practical manner for the above is to convert 3-phase secondary currentI₂ (I_(2u), I_(2v), I_(2w)) into (I_(α), I_(β), I₀) using Expression 1below on the 2-phase winding (α, β, 0) of the rotor.

$\begin{matrix}{\begin{pmatrix}I_{\alpha} \\I_{\beta} \\I_{0}\end{pmatrix} = {\sqrt{\frac{2}{3}}\begin{pmatrix}1 & {{- 1}/2} & {{- 1}/2} \\0 & {\sqrt{3}/2} & {{- \sqrt{3}}/2} \\{1/\sqrt{2}} & {1/\sqrt{2}} & {1/\sqrt{2}}\end{pmatrix}\begin{pmatrix}I_{u} \\I_{v} \\I_{w}\end{pmatrix}}} & \left\lbrack {{Expression}\mspace{20mu} 1} \right\rbrack\end{matrix}$

Next, based on Expression 2, (I_(α), I_(β), I₀) is transformed into arotating coordinate (I_(d), I_(q), I₀) using the rotor position θ_(s).This is nothing but the definition of a general dq transformation.

$\begin{matrix}{\begin{pmatrix}I_{d} \\I_{q} \\I_{0}\end{pmatrix} = {\sqrt{\frac{2}{3}}\begin{pmatrix}{\cos\;{\theta s}} & {{- \sin}\;{\theta s}} & 0 \\{\sin\;{\theta s}} & {{- \cos}\;{\theta s}} & 0 \\0 & 0 & 1\end{pmatrix}\begin{pmatrix}I_{\alpha} \\I_{\beta} \\I_{0}\end{pmatrix}}} & \left\lbrack {{Expression}\mspace{20mu} 2} \right\rbrack\end{matrix}$

The electric power system voltage V₁ detected by the system voltagedetector 21 is changed into scalar V by a system voltage detector 43,and the deviation between the voltage control command value V* and V isinputted into an alternating-current voltage controller 44 so as toobtain a d-axis current command value I_(d)*. The alternating-currentvoltage controller 44 shall preferably be an ordinary PI controller.

The primary current I₁ of the doubly-fed machine 4 (current through thestator winding) detected by a primary current detector 22 and theelectric power system voltage V₁ are changed into scalar power P by aneffective power detector 45, and the deviation between the power controlcommand value P* and P* is inputted into an effective power controller46 so as to obtain a q-axis current command value I_(q)*. The effectivepower controller 46 shall preferably be an ordinal PI controller.

Each deviation between the d-axis current I_(d) and d-axis currentcommand value I_(d)* and between the q-axis current I_(q) and q-axiscurrent command value I_(q)* are inputted into a current controller 47so as to obtain a d-axis voltage command value V_(d)* and q-axis voltagecommand value V_(q)*, respectively. The current controller 47 shallpreferably be an ordinary PI controller.

From these voltage command values and rotating position θ_(s) obtainedfrom the rotating position calculator 20, 2-phase voltage command valuesV_(α)* and V_(β)* are obtained respectively using an rotating coordinateinverse transformer 48, and also 3-phase voltage command values V_(u)*,V_(v)*, and V_(w)* are obtained respectively using a 2-phase/3-phaseconverter. To be concrete, an inverse transformation in Expression 1 andExpression 2 is performed, and then a dq transformation is performed.

The inverter 9 is controlled using these 3-phase voltage command valuesand gate signal generated by the PWM modulator 50.

Description about the rotating position calculator 20 is given below,using FIG. 2, FIG. 3 and FIG. 4. In these figures, the same symbol isgiven to the same component/part as in FIG. 1. FIG. 2 is an equivalentcircuit of the doubly-fed machine 4. The voltage equation of thisequivalent circuit is expressed as in Expressions 3, 4, 5, and 6.

$\begin{matrix}{V_{1} = {{\left( {R_{1} + {{j\omega}\; L_{1}}} \right){\overset{.}{I}}_{1}} + {\overset{.}{e}}_{0}}} & \left\lbrack {{Expression}\mspace{20mu} 3} \right\rbrack \\{V_{2}^{\prime} = {{\overset{.}{e}}_{0} - {\left( {R_{2}^{\prime} + {j\;\omega_{S}L_{2}^{\prime}}} \right){\overset{.}{I}}_{2}^{\prime}}}} & \left\lbrack {{Expression}\mspace{20mu} 4} \right\rbrack \\{{\overset{.}{e}}_{0} = {\frac{R_{M}j\;\omega\; L_{M}}{R_{M} + {j\;\omega\; L_{M}}}{\overset{.}{I}}_{0}}} & \left\lbrack {{Expression}\mspace{20mu} 5} \right\rbrack \\{{\overset{.}{I}}_{0} = {{{\overset{.}{I}}^{\prime}}_{2} - {{\overset{.}{I}}^{\prime}}_{1}}} & \left\lbrack {{Expression}\mspace{20mu} 6} \right\rbrack\end{matrix}$

A symbol marked with dot “{dot over ( )}” on its top is a scalar andmarked with dash “′” is a primary conversion value. In the expressions,j is an imaginary unit, L₁ is inductance, R₁ is primary resistance, L₂is secondary leak inductance, R₂ is secondary resistance, R_(M) isno-load loss resistance, L_(M) is excitation inductance, e₀ is inducedelectromotive force, I₀ is excitation current, ω is output frequency,and ω_(s) is slip frequency. FIG. 3 shows the vector diagram of theequivalent circuit. Finding the slip frequency ω_(s) enables to estimatethe rotor position. The slip frequency ω_(s) is obtained fromExpressions 3 to 6 and expressed as in Expression 7.

[Expression 7]

$\begin{matrix}{\omega_{S} = \frac{\frac{R_{M}j\;\omega\; L_{M}}{R_{M} + {j\;\omega\;{L_{M}\left( {{\overset{.}{I}}_{2}^{\prime} - {\overset{.}{I}}_{1}} \right)}} - {R_{2}^{\prime}I_{2}^{\prime}} - {\overset{.}{V}}_{2}^{\prime}}}{j\; L_{2}^{\prime}{\overset{.}{I}}_{2}^{\prime}}} & \left\lbrack {{Expression}\mspace{20mu} 7} \right\rbrack\end{matrix}$

Accordingly, the slip frequency ω_(s) can be obtained by inputting thedetected electric power system voltage V₁, primary current I₁, secondaryexcitation voltage V₂, secondary current I₂ and system frequency ω intothe rotating position calculator 20. When R<<L applies in Expressions 3to 7, the primary resistance and secondary resistance can be neglected.A way for finding the slip frequency ω_(s) using the secondaryexcitation voltage V₂ has been explained herein, but the voltage commandvalues V_(u)*, V_(v)* and V_(w)* can be used instead of the secondaryexcitation voltage V₂.

In order to decide the initial value of the slip frequency ω_(s) at therotor position θ_(s) in case the switch 101 is open, the transformationshown in FIG. 4 is performed. Firstly, position information is set toθ_(s0) by a time multiplier 201. Then, from the electric power systemvoltage V₁, voltage phase θ₁ is obtained by a phase detector 202. Thegenerator voltage V_(g) is then converted into V_(α) and V_(β) by a3-phase/2-phase converter 203 and, from these V_(α) and V_(β) and thevoltage phase θ₁, the d-axis voltage V_(d) and q-axis voltage V_(q) areobtained by a rotating coordinate transformer 204. Since the q-axisvoltage V_(q) becomes zero if the electric power system voltage V₁ andgenerator voltage V_(g) are at the same phase, it is compared with zeroand the difference is inputted into a phase adjuster 205. Byadding/subtracting its output to/from the position information θ_(s0),the phase of the rotor position θ_(s) is adjusted and accordingly, asthe electric power system voltage V₁ and generator voltage V_(g) at theswitch 101 become equal, the initial phase of the position informationθ_(s0) is decided. Then, when the switch 101 is closed, the output fromthe phase adjuster becomes zero because of V₁=V_(g) and accordingly theroutine for deciding the initial phase does not work in the normalgeneration mode. θ_(s) is decided as above.

FIG. 5 shows an embodiment wherein a windmill 501 is employed as thepower source of the present invention. Power source of the invention mayinclude wind power, hydraulic power, engine and turbine, but greatereffect of the invention is expected in the case of aerogeneration systemof which number of revolutions is very much variable.

According to the above embodiment of the present invention, wherein adoubly-fed machine is controlled without using a rotor position sensorsuch as resolver, it becomes possible to efficiently control thegenerator without using a rotor position sensor such as resolver on thedoubly-fed machine, and accordingly cost increase of a rotating machinecan be prevented. In addition, any noise suppression means is notnecessary for the rotor position sensor.

1. A rotating machine control unit that controls a rotating machineequipped with a stator, stator winding laid on the stator, rotor, androtor winding laid on the rotor; comprising a voltage detector fordetecting the voltage of the stator winding, current detector fordetecting the current of the stator winding, current detector fordetecting the current of the rotor winding, and voltage command valuecalculator for calculating a command value of the voltage to be appliedto the rotor winding; the voltage command value calculator calculating acommand value of the voltage to be applied to the rotor winding based onthe voltage of the stator winding detected by the voltage detector fordetecting the voltage of the stator winding, current of the statorwinding detected by the current detector for detecting the current ofthe stator winding, and current of the rotor winding detected by thecurrent detector for detecting the current of the rotor winding.
 2. Arotating machine control unit according to claim 1, further equippedwith a frequency detector for detecting the frequency of the voltage ofthe stator winding, wherein the calculator calculates a command value ofthe voltage to be applied to the rotor winding based on the frequency ofthe voltage of the stator winding detected by the frequency detector. 3.A rotating machine control unit that controls a rotating machineequipped with a stator, stator winding laid on the stator, rotor, androtor winding laid on the rotor; comprising a voltage detector fordetecting the voltage of the stator winding, current detector fordetecting the current of the stator winding, current detector fordetecting the current of the rotor winding, and rotor positioncalculator for calculating the information relating to the rotorposition; the rotor position calculator calculating the informationrelating to the rotor position based on the voltage of the statorwinding detected by the voltage detector for detecting the voltage ofthe stator winding, current of the stator winding detected by thecurrent detector for detecting the current of the stator winding, andcurrent of the rotor winding detected by the current detector fordetecting the current of the rotor winding.
 4. A rotating machinecontrol unit according to claim 3, further equipped with a voltagecommand value calculator for calculating a command value of the voltageto be applied to the rotor winding, wherein the voltage command valuecalculator calculates a command value of the voltage to be applied tothe rotor winding based on the information relating to the rotorposition calculated by the rotor position calculator.
 5. A powergeneration system equipped with a rotating machine, which is equippedwith a stator, stator winding laid on the stator, rotor, and rotorwinding laid on the rotor, control unit that controls the rotatingmachine, and power source that drives the rotor; comprising a voltagedetector for detecting the voltage of the stator winding, currentdetector for detecting the current of the stator winding, currentdetector for detecting the current of the rotor winding, and voltagecommand value calculator for calculating a command value of the voltageto be applied to the rotor winding; the voltage command value calculatorcalculating a command value of the voltage to be applied to the rotorwinding based on the voltage of the stator winding detected by thevoltage detector for detecting the voltage of the stator winding,current of the stator winding detected by the current detector fordetecting the current of the stator winding, and current of the rotorwinding detected by the current detector for detecting the current ofthe rotor winding.
 6. A power generation system according to claim 5,further equipped with a rotor position calculator for calculating theinformation relating to the rotor position, wherein the rotor positioncalculator calculated the information relating to the rotor positionbased on the voltage of the stator winding detected by the voltagedetector for detecting the voltage of the stator winding, current of thestator winding detected by the current detector for detecting thecurrent of the stator winding, and current of the rotor winding detectedby the current detector for detecting the current of the rotor winding.7. A power generation system according to claim 6, wherein the powersource utilizes wind power.
 8. A power generation system according toclaim 5, further equipped with a frequency detector for detecting thefrequency of the voltage of the stator winding, wherein the voltagecommand calculator calculates a command value of the voltage to beapplied to the rotor winding based on the frequency of the voltage ofthe stator winding detected by the frequency detector.
 9. A powergeneration system according to claim 8, wherein the voltage commandcalculator calculates a command value of the voltage to be applied tothe rotor based on the information relating to the rotor positioncalculated by a rotor position calculator.
 10. A power generation systemaccording to claim 5, wherein the power source utilizes wind power.